Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$136.34	3.558%	$141.191	$141.19	$141.20	$141.20
Purchase #2	$31.64	11.171%	$35.1745	$35.17	$35.15	$35.20
Purchase #3	$190.88	13.254%	$216.1792	$216.18	$216.20	$216.20
Purchase #4	$65.56	11.337%	$72.9925	$72.99	$73.00	$73.00
Purchase #5	$211.71	5.261%	$222.8481	$222.85	$222.85	$222.80
Purchase #6	$52.91	12.679%	$59.6185	$59.62	$59.60	$59.60
Purchase #7	$144.25	7.661%	$155.301	$155.30	$155.30	$155.30
7 purchase totals =	$833.29		$903.3048	$903.30	$903.30	$903.30